1. Field of the Invention
This invention relates to automated apparatus and a casting method for use therewith for retreading even very large tires, such as earth mover tires, with a polyurethane tread.
2. Prior Art
The present invention is in a new and unique automated apparatus and method for preparation of earth mover type tires for recapping, and recapping the tire with a polyurethane material. The recapping of the prepared tire takes place in a molding process, producing a finished recapped tire that is at least as cut resistant, and will have essential the same or better tire life, under like use conditions, as a new conventional rubber earth mover tire.
Heretofore, recapping of large, to very large, tires, such as an earth mover tire, have utilized rubber recapping techniques that have been difficult to practice, are labor intensive, and have not produced a tire capable of supporting heavy loads over rough terrain. Also, the quality and life expectancy such recapped heavy duty tires have varied greatly.
In practice, earlier tire retreading practices have involved cold rolling, adhesive bonding and application of pre-cured rubber. In a practice of such processes, new treads or tread sections are applied as with an adhesive onto a tire wherefrom the old tread has ground off, or roughened, and the tire and applied tread are heated to provide for a vulcanization of the tread to the tire. Such processes have not always provided a stable bonding of the applied tread material to the tire, and have often failed when subjected to heat, as a tire under load produces, causing a separation of the tire tread from tire crown or top surface.
Like earlier methods, the present invention includes the steps of inspecting a tire carcass to insure that it is suitable for retreading, and then grinding off the old tread to provide a specific tire profile. After grinding, the carcass is rechecked, particularly the tire ply's, belts and beads, to insure that the tire carcass is suitable for retreading. The carcass is then cleaned with an appropriate solvent entrained with air in a pressure spray.
Shortly after drying, the carcass is treated with a primer, preferably a primer known as Chemlock®, and is then allowed to dry for approximately fifteen minutes before an adhesive, preferably a Chemlock® adhesive is applied. The combination of the selected primer and adhesive provides for conditioning the carcass prepared tread area surface to securely and permanently bond to the tread of polyurethane material cast thereto. After application of the preferred primer and adhesive, the carcass is placed in an oven for approximately two hours at a temperature of approximately two hundred twenty five (225) degrees F. In practice, it is important to complete the process steps in a short period of time from the carcass grinding to where the carcass is coated with the preferred Chemlock® primer and Chemlock® adhesive and is ready to be heated.
Unique to the invention, after the required tire carcass heating, an inflatable tube is fitted into the carcass and is inflated to approximately nine (9) PSI, and the carcass is positioned in a mold that is heated to approximately one hundred eighty (180) degrees F. The mold, for practicing the process of the invention, provides for passing polyurethane materials into the mold cavity containing the carcass, off of an edge of a cone that directs an even distribution of the materials along the mold hub area and across the mold cavity to fill the mold cavity from bottom to top, forming the carcass tread, providing for pushing air from the mold cavity ahead of the pour. During the pour, the mold is rotated at a low RPM, to uniformly fill the mold and to provide for a homogeneous distribution of the materials in the mold cavity forming the carcass tread area. After approximately a fifteen (15) minute cure, the now retreaded tire carcass is removed from the mold and is post cured at a temperature of approximately one hundred seventy five (175) degrees F., for approximately twelve hours.
Prior to the present invention, retreading of a tire carcasses, particularly a large tire carcass with polyurethane materials, have not been successful, due to a failure to properly prepare and pour the selected polyurethane constituents so as to achieve a tread without voids or air pockets therein as does the practice of the method of the invention utilizing the apparatus of the invention, and in a single molding operation